High voltage cables that are used to transmit substantial quantities of electrical power either above ground or underground, frequently require splicing either during the installation in the field, or during down time, ie. repair. Several general techniques are known for handling such situations.
One method known to applicant is to provide a traditional cable splice, and to then take the spliced section of cable, insert it into a protective sheath or housing, and encapsulate the spliced cable segment. Such a technique and the apparatus therefore is disclosed and claimed in the Hankins et al U.S. Pat. No. 3,992,569 assigned to Hexcel Corporation.
Another technique is disclosed in Filreis et al U.S. Pat. No. 3,879,249 wherein a stiff resilient polymeric plastic sheet having a special surface of grooves and lattice work is provided and which sheet may be shaped to form a closure or mold about a splice. As a closure, dirt and dust are sealed out, and as a mold it can serve to shape insulating self-curing resinous compositions applied in a liquid form about the splice.
A very common technique employs a liquid potting method, which is reasonably economical but is primarily intended for low kilovolt transmissions because the materials available for the potting do not bond well to the cross-linked polyethylene or ethylene-propylene insulation used on high voltage cable. Applicant is aware however of a liquid slurry method claimed by Nakata in U.S. Pat. No. 3,996,081 issued Dec. 7, 1976 to be suitable for high voltage cable splice application.
One the of more popular techniques involves the use of tape wrapping followed by the application of high pressure by means of a hydraulic press and subsequent cure at elevated temperatures. This technique is not only costly, but slow, due to the careful wrapping process and the extended cure cycles. The emphasis today is on the development of in-the-field splicing techniques which hopefully can be provided quickly and cheaply while being suitable for high voltage applications. A paper covering Hexcel Corporation's research and development of a field molded splice for use on either crosslinked polyethylene or ethylene propylene rubber insulated solid dielectric cables was presented at the IEEE Southeast Conference in 1975. This paper relating to that company's Hotsplicer.TM. is incorporated herein by reference. A patent known by applicant that relates to such a tape wrapping technique, but not assigned to Hexcel is U.S. Pat. No. 3,970,488 issued July 20, 1976 to Nelson. As is recited therein, the generalized technique for making such a tapewrapped splice requires that the ends of the two cables to be spliced together are subjected to a plurality of steps. Firstly, they are prepared by removing a portion of the outer cable jacket, folding back the electrically conductive outer metallic shield, removing a portion of the underlying outer semiconducting screen, penciling the cable insulation down to the inner semiconducting screen, and removing a portion of the inner semiconducting screen to expose the central conductors. The two exposed central conductor end portions are next mechanically and electrically coupled together by means of a conventional connector, e.g. a connector sold in the trade as a Cadweld.TM. connector. The splice is next covered with one or more layers of semiconducting tape, and an electrically insulative jacket is molded onto the splice and adjacent regions of the cable insulation, after which a layer of semiconducting material is applied to the outer surface of the insulative mold, a layer of metal gauze material is wrapped around the semiconductive material, secured in place and soldered to the electrically conductive outer metallic shield and the splice is finished off with a layer of conventional electrician's tape.
The insulative jacket is molded to the cable splice by wrapping strips of semiconductive molding compound over the semiconducting tape, wrapping strips of electrically insulative thermosetting molding compound under heat and pressure into the mold chamber to soften the semiconducting and insulative molding compounds and bond them to the various surfaces with which they make contact, and curing the molded splice.